1. Field of the Invention
The present invention relates to a DRAM (dynamic random access memory) for a page memory and a controller used in a printer for a color multivalued image, a scanner for a color multivalued image, etc.
2. Description of the Related Art
A controller used in a printer for a color multivalued image, a scanner for a color multivalued image, etc. generally has a DRAM (dynamic random access memory) for a page memory within this controller. The controller has a large-sized circuit structure to transfer data at a high speed and perform complicated control operations according to various kinds of operating modes.
As mentioned above, various kinds of operating modes are required for the controller. For example, when an object unit is constructed by a printer, there is an operating mode in which output processing of data transmitted to the printer is performed and three primary colors of yellow, magenta and cyan (YMC) of light are used as color objects and data of these three primary colors are simultaneously transmitted in a data transfer method. In contrast to this, when the object unit is constructed by a scanner, there is another operating mode in which input processing of data transmitted to the scanner is performed and different three primary colors of red, green and blue (RGB) of light are used as color objects and data of these three primary colors are transferred every one color in a data transfer method.
A memory (DRAM) having a large capacity is required for this controller. For example, this memory has the following contents.
______________________________________ paper size A3 A3 image density 400 dpi 400 dpi gradation 2.sup.2 values 2.sup.8 values color data 32 MB 128 MB ______________________________________
In this case, the color data are provided in the case of YMCK.
However, in the general DRAM for a page memory and the general controller for each of a printer and a scanner, the width of a data bus of the used DRAM is fixedly set. Therefore, a using method of the DRAM is fixed so that there is a problem of low extendability that this DRAM cannot be easily used in an extended way. For example, when a DRAM of 32 MB (constructed by 16 DRAMs of 15M bits) is mounted, it is possible to select a first access method for providing size A3 and color gradation of 2.sup.2 values, and a second access method for providing size A5 and color gradation of 2.sup.8 values. In the first access method, color data are accessed in a unit of 2 bits every color. In the second access method, color data are accessed in a unit of 8 bits every color. When the first or second access method is selected, it is impossible to use the DRAM in another access method.
Further, since the width of a data bus of the used DRAM is fixedly set, it is necessary to dispose a complicated bus-converting circuit for performing a high speed access operation by using a two-bank interleaving method. In the two-bank interleaving method, the DRAM is physically divided into two memory sections and data of these two memory sections are alternately accessed.
As mentioned above, three primary colors (YMC) of light or different three primary colors (RGB) of light are used. In the case of YMC, white color is provided when all color data show value "0". In contrast to this, in the case of RGB, white color is provided when all color data show value "1". Accordingly, logics of the white data are reverse to each other in the cases of YMC and RGB. Therefore, processings corresponding to the reverse logics of the white data such as clear processing of DRAM data, etc. are performed by using software, thereby increasing a processing time of the DRAM.